There are two types of Kelvin waves, coastal and equatorial, and they are
both gravity driven and non-dispersive. They are often excited by an
an abrupt change in the overlying wind field, such as the shift in the
trade winds at the start of El Niño.

Equatorial waves propagate to the east in the northern hemisphere,
using the equator as a wave guide.
Coastal Kelvin waves propagate around the northern hemisphere oceans
in a counterclockwise direction using the coastline as a
wave guide.
These waves, especially the surface waves
are very fast moving, typically with speeds of ~2.8 m/s, or about 250 kilometers
in a day.
A Kelvin wave would take about 2 months to cross the Pacific from New Guinea to South America.